What occurrence defines the end of the protostar phase of a star's life and the start of the main-sequence phase?

Calculate the momentum of a 1600 kg car traveling at 20 m/s

A car traveling on a flat (unbanked), circular track accelerates uniformly from rest with a tangential acceleration of 1.85 m/s2. The car makes it one quarter of the way around the circle before it skids off the track.

A (n) 1.7 kg skateboard is coasting along the pavement at a speed of 2.33 m/s when a (n) 0.915kg cat drops from a tree vertically downward onto the skateboard. What is the speed of the skateboard-cat combination? Answer in units of m/s.

Which object absorbs the most visible light? O a clear bowl O a white rock O a black t-shirt O a red apple

What does the variable a meand in physics

Would time travel mean that parallel universes would be created off our linear time sequence to ensure the universe doesn't collapse itself because of significant events being drastically changed in the way it shapes the universe?

What is the central core of hair

A star with the same mass of the sun has a newly discovered planet whose semi-major axis of 2.48 au and an eccentricity of 0.08. what is the aphelion distance of the new planet

What does a hurricane hunter do

Why is fluorine special in terms of electronegativity?